Manufacture of transparent flexible sheets

ABSTRACT

Transparent sheets impermeable to liquids and gases are obtained from solutions of gelatine containing as softening agent one or more sulphonic acids of higher aliphatic alcohols or sulphonic salts thereof.  The higher alcohols referred to are those containing at least 16 carbon atoms and up to 22 carbon atoms.  The sheets are obtained by extrusion or by casting solutions of gelatine and the softening agent.  The solidified sheets may be treated with an aqueous solution of glycerine.  They may be coated on both sides with a cellulose ester solution containing tanning agents such as formalin, chromates, tannin, quinone, or glycol.  These additions also effect a more permanent adherence between the gelatine base and the cellulose ester coatings.

I ?atented Apr. &, 193$ STATS MANUFACTURE OF TRANSPARENT I FLEXIBLESHEETS Ernest Saraga, Bucharest, Rumania 1 Claim. (CI. 91-68) I Thepresent invention relates to the manufacture of flexible transparentsheets, and more particularly to the manufacture of sheets of this kindwhich are highly resistant and'are entirely *5 impermeable to liquidsand gases.

The manufacture of transparent sheets-by the employment of gum,gelatine, cellulose or other similar materials is known per se. Theknown methodof manufacture consists in adding to the initial material inquestion a softening agent, such as-Turkey red oil or salts of thelatter, or

. adding glycerine directly. In quite recent time it has been proposedin addition to this to coat the said sheets on their two faces with-athin coating of a cellulose ester with the object of rendering themperfectly impermeable.

The present invention has for'its principal obiect the provision of anovel' process for the manufacture of transparent sheets, whereingelatine is used as the base or starting material, the

said sheets being intended to replace the known sheets made of celluloseor of acetyl cellulose, and

the said process offering the advantage that it renders the manufacturemore economical and provides a means for obtaining highly resistantsheets which are entirely impermeable to water and which are greatlysuperior to the similar sheets obtained by the processes hitherto em-Ployed.

Thesaid sheets are manufactured in similar manner to that which is knownper se, but the process according to the invention presents, as

compared with the known processes, the follow- -ing characteristicdifierences:

1. The gelatine employed as the base or starting v material for themanufacture of the sheets is mixed or combined with a predeterminedqu'an: tity of aknown softening agent such as a sulphonate of a higheraliphatic alcohol.

40 2. This mixture is converted into sheets by any known method, such asextrusion through a slit intoa coagulating bath, or pouring on to aplate, and according to the invention an aqueous solution of glycerineis poured on to the sheets before they have become dry, this being donewith the object of preventing an excessive desiccating or drying of saidsheets. In the processes hitherto employed, the glycerine was directlydissolved in the starting material, whereas experiments which have beencarried out have demonstrated that 5 v by treating the already formedsheets with a solution of glycerine, according to the process comprisedin the subject matter of the present invention, a very greatly superiorresult to that obtained by the hitherto known processes is ob- 10tained. I

3. The sheets thus treated are finally coated on both sides with a thincoating of cellulose ester (for'example by impregnation with the esterin question),.to which is added a tanning agent, 15 such as Formalin, achromate, tannin, quinone, or the like. In this way the sheets arerendered impermeable andthe structure of the superficial molecules ofthe two sides of each sheet is at the same time modified in such mannerthat perfect 0 adherence of the two coatings of cellulose ester with thecorresponding sides is obtained.

By the aid of the process according to the in.- vention thin transparentsheets are obtained which possess a much higher resistance than 25 thatof the sheets manufactured according to the known processes andthanlthat of the cellulose or acetyl cellulose sheets. The sheetsmanufactured according to the invention are, moreover,

characterised by perfect'adhesion of the two 30 coatings which areapplied on the gelatine sheets, in such manner that the possibility oftheir dissolving incontact with water,- moisture or other liquids isentirely eliminated.

I claim: 35

In the manufacture of flexible highly resistant transparent sheets ofgelatine treated with a small quantity of at least one sulphonate of ahigher aliphatic alcohol, the steps of: treating the surfaces of saidsheets with an aqueous solution 4 of glycerine to maintain said sheetsin a soft and moist condition; and impregnating said sheets with amixture composed of a cellulose ester and a tanning agent.

ERNEST SARAGA. as l

